System And Method For The Treatment Of Heart Tissue

ABSTRACT

A device is disclosed for locating and treating an infarct scar in a heart. The device includes a catheter, a collapsible heater and energizing means connected to the collapsible heater for energizing the collapsible heater to raise the temperature of the infarct scar to a temperature sufficient to reduce the surface area of the infarct scar.

STATEMENT OF RELATED APPLICATION

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 11/035,657 filed Jan. 14, 2005, in the name ofinventor Michael D. Laufer, entitled “System And Method For TheTreatment Of Heart Tissue.”

TECHNICAL FIELD

The present invention is related generally to the medical treatment ofthe heart, including modification of heart tissue for the treatment ofmyocardial infarction.

BACKGROUND

As is well known, the heart has four chambers for receiving and pumpingblood to various parts of the body. During normal operation of theheart, oxygen-poor blood returning from the body enters the rightatrium. The right atrium fills with blood and eventually contracts toexpel the blood through the tricuspid valve to the right ventricle.Contraction of the right ventricle ejects the blood in a pulse-likemanner into the pulmonary artery and each lung. The oxygenated bloodleaves the lungs through the pulmonary veins and fills the left atrium.The left atrium fills with blood and eventually contracts to expel theblood through the mitral valve to the left ventricle. Contraction of theleft ventricle forces blood through the aorta to eventually deliver theoxygenated blood to the rest of the body.

Myocardial infarction (i.e., heart attack) can result in congestiveheart failure. Congestive heart failure is a condition wherein the heartcan not pump enough blood. When patients have a heart attack, part ofthe circulation to the heart wall muscle is lost usually due to a bloodclot which dislodges from a larger artery and obstructs a coronaryartery. If the clot is not dissolved within about 3 to 4 hours, themuscle which lost its blood supply necroses and subsequently becomes ascar. The scarred muscle is not contractile, and therefore it does notcontribute to the pumping ability of the heart. In addition, the scarredmuscle is elastic (i.e., floppy) which further reduces the efficiency ofthe heart because a portion of the force created by the remaininghealthy muscle bulges out the scarred tissue (i.e., ventricularaneurism) instead of pumping the blood out of the heart.

Congestive heart failure is generally treated with lots of rest, alow-salt diet, and medications such as A.C.E. inhibitors, digitalis,vasodilators and diuretics. In some myocardial infarction instances, thescarred muscle is cut out of the heart and the remaining portions of theheart are sutured (i.e., aneurismechtomy). In limited circumstances aheart transplant may be performed. The condition is always progressiveand eventually results in patient death.

Collagen-containing tissue is ubiquitous in normal human body tissues.Collagen makes up a substantial portion of scar tissue, includingcardiac scar tissue resulting from healing after a heart attack.Collagen demonstrates several unique characteristics not found in othertissues. Intermolecular cross links provide collagen-containing tissuewith unique physical properties of high tensile strength and substantialelasticity. A property of collagen is that collagen fibers shorten whenheated. This molecular response to temperature elevation is believed tobe the result of rupture of the collagen stabilizing cross links andimmediate contraction of the collagen fibers to about one-third of theiroriginal length. If heated to approximately 70 degrees Centigrade, thecross links will again form at the new dimension. If the collagen isheated above about 85 degrees Centigrade, the fibers will still shorten,but crosslinking will not occur, resulting in denaturation. Thedenatured collagen is quite expansile and relatively inelastic. Inliving tissue, denatured collagen is replaced by fibroblasts withorganized fibers of collagen than can again be treated if necessary.Another property of collagen is that the caliber of the individualfibers increases greatly, over four fold, without changing thestructural integrity of the connective tissue.

U.S. Pat. No. 6,071,303 teaches a device and method for treating infarctscar tissue of a mammalian heart by selectively heating the infarct scarto reduce the size of the scar tissue surface area, increase thecross-section of the scar tissue, stiffen the floppy portion of the scartissue, reduce the ventricular systolic wall tension, and increase theoverall pumping efficiency of the infarcted heart by eliminating theventricular aneurism or dilated ventricle, if present. FIG. 1illustrates an embodiment of the device taught in U.S. Pat. No.6,071,303.

Referring to FIG. 1, there is illustrated a heart 10 having an infarctedregion or portion 12. The infarcted portion 12 of the heart can beaccessed with conventional open chest surgery. A positive electrode 14and negative electrode 16 are applied externally to a portion of theinfarcted portion 12 to induce resistive heating in the infarct scar inthe desired treatment area 18 when energy is applied across theelectrodes. Alternatively, the positive and negative electrodes can beinserted into the infarcted scar. The positive and negative electrodesfunction as a heating element as they are energized to raise thetemperature of the scar in the desired treatment area 18 to a controlledtemperature sufficient to reduce the surface area of the scar withoutablating the scar tissue or damaging the healthy tissue surrounding theinfarcted portion 12.

U.S. Pat. No. 6,071,303 also teaches other appliances for applyingradiant energy or thermal energy, or to otherwise heat the infarctedtissue and reduce the area of the infarcted tissue. For example, asshown in FIG. 2 a radio-frequency generator 20 and heating elementapplicator 22 can be used. When the heating element 24 of the applicator22 is positioned at the desired treatment site, the radio-frequencygenerator 20 is activated to provide suitable energy, preferably at aselected frequency in the range of 10 megahertz to 1000 megahertz, toheat the scar tissue to a temperature sufficient to reduce the surfacearea of the scar without ablating the scar tissue or damaging thehealthy tissue surrounding the infarcted area 12.

It should be understood that the devices taught in U.S. Pat. No.6,071,303 are located external to the heart. However, I have found thatin certain circumstances it can be preferable to apply heat in theinternal surface of the heart. For example, in some cases the scartissue is more severe or larger or both, within the heart than on thesurface. Also, the use of the devices taught in U.S. Pat. No. 6,071,303can require conventional open chest surgery. However, in some cases itis desirable for the surgeon to gain access to the patient's heart bycatheterization.

OVERVIEW

It is an object of the present invention to provide a means to applyheat to a patient's infarct scar using a device deployed by acatheterization procedure so that the device is located inside theheart.

It is another object of the present invention to provide a means toapply heat to a patient's infarct scar using a device located inside theheart to raise the temperature of the scar in the desired treatment areato a controlled temperature sufficient to reduce the surface area of thescar without ablating the scar tissue or damaging the healthy tissuesurrounding the infarcted portion.

It is another object of the invention to provide a means to locate apatient's infarct scar.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention.

In the drawings:

FIG. 1 is a view of a conventional system for the treatment of infarctedheart tissue.

FIG. 2 is a view of another conventional system for the treatment ofinfarcted heart tissue.

FIG. 3 is a view of a system for the treatment of infarcted heart tissueaccording to a preferred embodiment of the present invention, withportions removed for clarity and to show internal components.

FIG. 4 is a view of the system shown in FIG. 3, taken along line 4-4 ofFIG. 3

FIG. 5 is a view a portion of the system of FIG. 3 illustrating itsoperation.

FIG. 6 is another view of the system of FIG. 3 illustrating itsoperation as the heart contracts.

FIG. 7 is another view of the system of FIG. 3 illustrating itsoperation as the heart relaxes.

FIG. 7 a is view of an alternative embodiment.

FIG. 7 b is another view of the alternative embodiment of FIG. 7 a.

FIG. 8 is an alternative embodiment of the present invention.

FIG. 9 is a view of the embodiment of FIG. 8 with the mylar removed.

FIG. 10 is a view of another embodiment with part not shown toillustrate internal components.

FIG. 11 is a view of another embodiment.

FIG. 12 is a view of still another embodiment, shown with a portion of apatient to illustrate operation of the device.

FIG. 13 is a view of still another embodiment.

DETAILED DESCRIPTION

Embodiments of the present invention are described herein in the contextof a system and method for treatment of infarcted heart tissue. Those ofordinary skill in the art will realize that the following detaileddescription of the present invention is illustrative only and is notintended to be in any way limiting. Other embodiments of the presentinvention will readily suggest themselves to such skilled persons havingthe benefit of this disclosure. Reference will now be made in detail toimplementations of the present invention as illustrated in theaccompanying drawings. The same reference indicators will be usedthroughout the drawings and the following detailed description to referto the same or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

Turning to FIGS. 3-7, the first embodiment of the present inventionincludes a catheter 31 and a collapsible heater 30 attached to thedistal end of the a flexible cable 41. The cable 41 is located in thelumen of the catheter 31 so that the cable 41 can slide therein.

The collapsible heater 30 comprises a ring 40 mounted to the distal endof the flexible cable 41, and a plurality of struts 42 are mounted withtheir proximal ends affixed to the ring 40. The struts 42 are flexibleand spring-like so that they can flex toward and away from the centeraxis of the ring 40. At the distal ends of the struts 42 a flexible wire44 is mounted in a circular configuration to limit the outward motion ofthe distal ends of the struts 42. A center electrode 46 is located alongthe center axis of the ring 40, and a plurality of outside electrodes 48are mounted to the wire 44. The center electrode 46 and outsideelectrodes 48 are electrically connected to a radio-frequency generator50 that is located outside the patient's body. A mylar sheet 52 forms abag-like structure which is located around the collapsible heater tocompletely enclose the struts 42, wire 44 and electrodes 46 and 48, andthe proximal end of the mylar sheet 52 is connected to the ring 40. (Themylar sheet 52 is shown in FIGS. 6 and 7 but omitted from FIGS. 3 and 4to permit the internal components to be seen.) Alternatively, theelectrodes may be an integral part of the mylar sheet 52, with oneconfiguration that the electrodes are printed in electrically-conductiveink on the mylar. Also, the mylar itself can act as a restraint on thestruts 42, obviating the need for wire 44.

An attachment member 70 extends through the cable 41 and from the distalend of the collapsible heater 30. The attachment member 70 comprises athin, flexible rod 72 which extends through a lumen in the cable 41 andthrough a lumen in the center electrode 46. A corkscrew-shaped connector74 is located at the distal end of the rod 72, and a handle 76 islocated at the proximal end of the rod 72 so that a user can rotate thehandle 76 to cause the corkscrew-shaped connector 74 to rotate.

To operate the device shown in FIGS. 3-7, first a physician introduces acatheter 31 into a patient so that the distal end of the catheter 31 islocated in the interior of the patient's heart according to conventionalprocedures. The physician then inserts the collapsible heater 30 intothe proximal end of the catheter 31 so that the collapsible heater 30 isin the collapsed orientation in which the struts 42 are substantiallyparallel to each other. This can be accomplished with or without aconventional guidewire. In the case a guidewire is used, a lumen 56 isprovided which extends through the cable 41 and through the centerelectrode 46 of the RF heater. The physician then pushes the cable 41 toforce the collapsible heater 30 through the catheter 31 until thecollapsible heater 30 is near the distal end of the catheter, as shownin FIG. 5. As the physician continues to push the cable 41, thecollapsible heater 30 exits the distal end of the catheter 31 andexpands to the deployed orientation as shown in FIG. 3.

When the collapsible heater 30 is positioned at the desired treatmentsite, the radio-frequency generator 50 is activated to provide suitableenergy, preferably at a selected frequency in the range of 10 megahertzto 1000 megahertz, to heat the scar tissue to a temperature sufficientto reduce the surface area of the scar without ablating the scar tissueor damaging the healthy tissue surrounding the infarcted area 12.Preferably, the emitted energy is converted within the scar tissue intoheat in the range of about 40 degrees Celsius to about 75 degreesCelsius, more preferably in the range of about 60 degrees Celsius toabout 65 degrees Celsius. The radio-frequency energy is preferablyapplied at low power levels (e.g., 1 to 20 watts). Suitableradio-frequency power sources are readily commercially available.Moreover, the radio-frequency energy can be multiplexed by applying theenergy in different patterns over time as appropriate. In oneembodiment, the radio-frequency generator 20 has a single channel,delivering approximately 1 to 20 watts of energy and possessingcontinuous delivery capability. A feedback system can be connected tothe collapsible heater 30 for detecting appropriate feedback variablesfor temperature control. For example, temperature sensing by way of athermocouple 54 mounted on the distal end of the center electrode 46 maybe incorporated to provide feedback to modulate power from the RFgenerator 50 or other energy source through a feedback loop 56 and/orsoftware within the generator 50 or connector/cable. Alternatively,other feedback systems could be employed, e.g. a thermistor could bemounted to the mylar sheet 52 in a location to contact the infarct scar.

Turning now to FIGS. 6 and 7 other aspects of the present invention areshown. It should be understood that it is important to locate thecollapsible heater 30 in close proximity to or touching the infarctedportion 12. It should also be understood that in some cases theinfarcted portion 12 is somewhat thinner and weaker than the adjacent,healthy portion of the heart, and consequently when the heart musclescontract the infarcted portion bulges outward from its normalconfiguration, as indicated in FIG. 6. When this occurs there tends tobe blood flow toward the bulge as suggested by arrows 60. Accordingly,the collapsible heater 30 acts like a sail and is carried toward thebulge by the blood flow. Thus the collapsible heater 30 can be said tobe self-positioning. It should be understood that to facilitate thisself-positioning feature at least the flexible cable 41 and in somecases, both the flexible cable 41 and the catheter 31, must beconsiderably different from a conventional catheter. Specifically, aconventional catheter is relatively rigid and can include structures topermit a physician to manipulate the distal end of the catheter from alocation external to the patient. Such a catheter can be called a“steerable” catheter. In contrast, in the present invention, at leastthe flexible cable 41 and in some cases, both the flexible cable 41 andthe catheter 31 must be quite flexible to allow the blood flow to movethe collapsible heater. For this reason, the flexible cable is shown inFIGS. 6 and 7 as somewhat limp, and the catheter 31 can be understood tobe a flexible tube, without the components often found in a conventionalsteerable catheter which to permit a physician to manipulate the distalend of the catheter from a location external to the patient. Similarly,the flexible tube does not include components which permit a physicianto manipulate the distal end of the flexible tube from a locationexternal to the patient.

As the heart continues to pump, the collapsible heater is carried towardthe infarcted portion 12 until the distal end of the corkscrew-shapedconnector 74 contacts the infarct. Then the physician can rotate thehandle 76 to rotate the connector so that the connector engages theinfarct and pulls the collapsible heater into contact with the infarct,shown in FIG. 7. Then when the physician applies RF energy to the heater30 the energy is applied directly to the infarct and is not dissipatedinto blood between the heater 30 and the infarct 12 as would be the caseif the heater 30 were spaced apart from the infarct 12. When theprocedure is complete, the physician rotates the handle 76 to releasethe connector 74 from the infarct 12.

Turning now to FIGS. 7 a and 7 b another embodiment is shown. Theembodiment of FIGS. 7 a and 7 b comprises a heater locating system 110which comprises a heater 112 which is similar to the collapsible heater30, except that the heater 112 includes an ultrasonic crystal 114mounted at the distal end of the center electrode 46. The heaterlocating system 110 further comprises a locating device 116 including anultrasonic crystal array which is located outside the patient 106 andwhich allows a physician to determine the location of the ultrasoniccrystal 114. The system of FIGS. 7 a-7 b further includes a steerablecatheter 120, and the heater 112 is mounted to the distal end of thesteerable catheter 120. In operation, the heater 112 is introduced intothe patient's heart in the same way as is the collapsible heater 30 asdiscussed above. The physician uses the locating device 116 to monitorthe location of the ultrasonic crystal and the heater 112, and thephysician uses the steerable catheter 120 to locate the heater adjacentthe infarct 12. Then the physician uses the heater 112 to heat theinfarct scar in the same way as the collapsible heater 30 as discussedabove and illustrated in FIGS. 6 and 7.

It should be understood that other types of monitoring and locatingsystems could be used by a physician to monitor the location of a heaterand locate the heater adjacent an infarct scar.

FIGS. 8-10 show another embodiment which includes an alternative meansto connect a heater 78 to the infarct 12. In this embodiment, the heater78 is similar to heater 30 in most respects, except that in heater 78the attachment member 70 is absent, instead a plurality of hooks 80 aredisposed around the periphery of the wire 44. The hooks 80 are concavewith their middle portions being closer to central axis of the heater 30than their top and bottom portions. In operation, the collapsible heater78 with hooks 80 is pushed through the catheter 31 until it nears thedistal end of the catheter. At this point the distal end of the catheter31 is positioned adjacent the infarct. Then as the collapsible heaterexits the distal end of the catheter 31, as shown in FIG. 9 the struts31 begin to move away from their collapsed orientation and the hooks 80engage the infarct as shown in FIG. 10. The physician then heats theinfarct as explained above. Thereafter, when heating has been completed,the hooks 80 are released from the infarct 12 by sliding the distal endof the catheter over the struts 42, which causes the hooks 80 todisengage from the infarct 12 to allow removal of the collapsible heaterfrom the heart.

Optionally, as shown in FIG. 10, in heater 78 strain gauges 82 areconnected to the struts 42 and the ring 40 to measure flexion of thestruts relative to the ring 40, and signals from the strain gauges arecarried by wires, not shown, to a meter 84 located outside the patient.(In FIG. 10 the mylar sheet 52 is not shown, in order to illustrateinternal components.) This permits measurement of the extent to whichthe infarcted portion has been treated. Specifically, when the hooks 80are affixed to infarcted portion the strain measured by the strain gauge82 is recorded. Then when heat is applied to the infarcted portion 12the infarcted portion shrinks which causes the distal ends of struts 42to be drawn toward each other, which in turn causes a change in thestrain measured by the strain gauges 82. When the measured strain stopschanging it is known that the infarcted portion is completely treatedand will not shrink further. At this time heating is discontinued andthe heater 78 is removed.

Turning now to FIG. 11 one example of an alternative heater is shown.According to the embodiment shown in FIG. 11 a collapsible heater 90 issimilar to heater 78 in most respects, except that in heater 90 thereare no center electrode 46 or outside electrodes 48. Rather, there is aninfrared light source 92 which is connected to a controllable powersupply, not shown, to heat the infarct region.

Turning now to FIG. 12 another embodiment is shown. It should beunderstood that in the embodiments discussed above, the self-locatingaspect of the invention is applied to locating a heater. On the otherhand, in the embodiment of FIG. 12 the self-locating feature is notemployed to locate a heater but is employed to locate the infarct 12 forother purposes. In certain medical procedures it is important for aphysician to be able to accurately locate an infracted region of theheart. One example is to perform electro physiologic ablation using aconventional device. Accordingly, the embodiment of FIG. 12 comprises aninfarct locator 100 which is similar to the collapsible heater 30,except that the infarct locator 100 does not include heating elements,and the infarct locating system 102 comprises an acoustic imaging device104 which is located outside the patient 106 and which allows aphysician to determine the location of the infarct locator 100. Inoperation, the infarct locator 100 is introduced into the patient'sheart in the same way as is the collapsible heater 30 as discussedabove. Then the infarct locator is located adjacent the infarct 12 byits self-positioning features in the same way as is the collapsibleheater 30 as discussed above and illustrated in FIGS. 6 and 7. Thephysician can use the acoustic imaging device 104 to monitor thelocation of the infarct locator 100, or other means such as X-rayimaging can be used.

Turning now to FIG. 13 another embodiment is shown. This embodiment issimilar to the embodiment shown in FIGS. 3-7. However, the FIG. 13embodiment includes a system to assist in locating the infarct scar bymeasuring certain electrical properties of the heart tissue. It shouldbe understood that an infarct scar has resistivity which is greater thanthat of normal heart muscle and conversely the conductivity of theinfarct scar is less than that of normal heart muscle. Moreover, whereasnormal heart muscle generates electrical signals, an infarct scargenerates no electrical signals. Accordingly, the device of FIG. 13measures electrical properties of the heart tissue to determine theconductivity, the resistivity or the electrical signals generated by thetissue to thereby ascertain whether the tissue is normal or an infarctscar. To accomplish this a conventional electrical monitoring system 130is connected to the center electrode 46 and to the outside electrodes48, and the electrodes 46 and 48 are used are used to transduceelectrical signals as necessary.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this disclosure that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.The invention, therefore, is not to be restricted except in the spiritof the appended claims.

1. A method for treating an infarct scar in a heart, comprising thesteps of: introducing a catheter into the heart; placing a heatingelement through the catheter and adjacent to the infarct scar; and,energizing the heating element to raise the temperature of the infarctscar.
 2. A method according to claim 1 wherein the step of energizingthe heating element comprises controllably energizing the heatingelement to raise the temperature of the scar to a controlledtemperature.
 3. A method according to claim 1 further comprising thesteps of repeating the placing and energizing steps to treat the entireinfarct scar surface.
 4. A method according to claim 1 wherein the stepof energizing the heating element raises the temperature of the infarctscar to a temperature sufficient to reduce the surface area of theinfarct scar.
 5. A method according to claim 1 wherein said heatingelement is placed in contact with the infarct scar.
 6. The method ofclaim 1 wherein the heating element is energized by applying radiofrequency energy.
 7. The method of claim 1 wherein the heating elementis energized by resistive heating.
 8. The method of claim 1 wherein thescar is energized to a temperature in the range of about 40 degreesCelsius to about 75 degrees Celsius.
 9. A device for treating an infarctscar in a heart, comprising: a catheter; a collapsible heater connectedto said catheter; and, energizing means connected to said collapsibleheater for energizing at least a portion of the collapsible heater toraise the temperature of the infarct scar.
 10. A device according toclaim 9 wherein said collapsible heater is connected to the distal endof a cable.
 11. A device according to claim 10 wherein said cable isslideable in a lumen of said catheter.
 12. A device according to claim 9wherein said collapsible heater is constructed and arranged to beslideable through the lumen of said catheter when in a collapsed state.13. A device according to claim 9 wherein said collapsible heater isconstructed to expand to a deployed state in which said collapsibleheater occupies greater volume than when said collapsible heater is inthe collapsed state.
 14. A device according to claim 9 wherein saidcollapsible heater comprises a feedback system to enable a user todetermine the extent to which heating of the scar has been completed.15. A device according to claim 14 wherein said collapsible heatercomprises struts and said feedback system comprises strain gaugesconnected to said struts.
 16. A device according to claim 9 wherein saidcollapsible heater further comprises: a support connected to saidcatheter; a plurality of struts connected to said support; a mylar sheetconnected to said struts; and, a plurality of electrodes connected tosaid struts.
 17. A device for treating an infarct scar in a heart,comprising: a catheter; a self-positioning heater connected to saidcatheter; and, energizing means connected to said collapsible heater forenergizing at least a portion of the collapsible heater to raise thetemperature of the infarct scar.
 18. A device according to claim 17wherein said self-positioning heater is constructed to be movable byblood flow within the heart.
 19. A device according to claim 17 whereinsaid self-positioning heater comprises a flexible cable connected tosaid catheter.
 20. A device according to claim 18 wherein said selfpositioning heater comprises a collapsible heater which can expand to adeployed state having a volume greater than when in its collapsed state.